Devices like iPads and light bulbs use electrons to send information, but in nature, electrical signaling occurs with ions and protons.

Scientists at University of Washington have built a novel transistor that uses protons, opening the door to a new class of bio-compatible solid-state devices that can potentially communicate directly with living things.

On the left is a colored photo of the UW device overlaid on a graphic of the other components. On the right is a magnified image of the chitosan fibers. The white scale bar is 200 nanometers. Credit: UW

Researchers have been exploring for ways to connect devices with the human body's processes for biological sensing or for prosthetics. While gains have been made in bio-compatible electronic devices that can flex, stretch and function in wet environments, such as the human body, the same cannot be said about how they communicate with living tissue.

"So there's always this issue, a challenge, at the interface – how does an electronic signal translate into an ionic signal, or vice versa?" said lead author Marco Rolandi, a UW assistant professor of materials science and engineering. "We found a biomaterial that is very good at conducting protons, and allows the potential to interface with living systems."

Electronic devices typically communicate using electrons, which are negatively charged particles. In the body, protons activate "on" and "off" switches and are key players in biological energy transfer, whereas ions open and close channels in the cell membrane to pump things in and out of the cell. Humans and other animals use ions to flex their muscles and transmit brain signals.

"A machine that was compatible with a living system in this way could, in the short term, monitor such processes. Someday it could generate proton currents to control certain functions directly," notes a release.

The first step toward this type of control is a transistor that can send pulses of proton current and the UW prototype is the first one to demonstrate that it can. The device is a field-effect transistor, which includes a gate, a drain and a source terminal for the current. It measures about 5 microns wide, roughly a twentieth the width of a human hair, and uses a modified form of the compound chitosan originally extracted from squid pen, a part of the squid that remains from its shelled ancestors. The team found that chitosan works remarkably well at moving protons and is easy to source.

"In our device large bioinspired molecules can move protons, and a proton current can be switched on and off, in a way that's completely analogous to an electronic current in any other field effect transistor," Rolandi said.

Applications for the proton transistor are still a long way off and include direct sensing of cells in a laboratory. Once a bio-compatible version is available --the current prototype has a silicon base and could not be used in a human body--it could be implanted directly in living things to monitor, or even control, certain biological processes directly, say the scientists.

The study "A polysaccharide bioprotonic field-effect transistor" is published online this week in the interdisciplinary journal Nature Communications.